The present study reports the photo-Fenton degradation of phenolic compounds (phenol, 2-chloro-4-nitrophenol and 4-chloro-2-nitrophenol) in aqueous solution using mesoporous Cu/Al₂O₃–MCM-41 nanocomposite as a heterogeneous photo-Fenton-like catalyst. The in situ incorporation of mesoporous Al₂O₃ (MA) into the framework of MCM-41 (sol–gel method) forms Al₂O₃–MCM-41 and wetness impregnation of Cu(II) on Al₂O₃–MCM-41 generates mesoporous Cu/Al₂O₃–MCM-41 composite. The effects of pH and H₂O₂ concentration on degradation of phenol, 2-chloro-4-nitrophenol and 4-chloro-2-nitrophenol are studied. Kinetics analysis shows that the photocatalytic degradation reaction follows a first-order rate equation. Mesoporous 5 Cu/Al₂O₃–MCM-41 is found to be an efficient photo-Fenton-like catalyst for the degradation of phenolic compounds. It shows nearly 100% degradation in 45 min at pH 4. The combined effect of small particle size, stabilization of Cu²⁺ on the support Al₂O₃–MCM-41, ease reducibility of Cu²⁺ and visible light activeness are the key factors for quick degradation of phenolic compounds by Cu/Al₂O₃–MCM-41.